The present application relates to mixing signals from two different frequency bands.
In some devices, such as wireless telephones, it is often desirable to have circuitry that can operate in two radio frequency (RF) bands (or dual bands) while using a common intermediate frequency and common intermediate frequency (IF) circuitry. Unfortunately, a potential problem with such mixing circuitry is signal loss. Another potential problem is that the mixing circuitry may need a large number of components, thereby increasing the cost, power consumption and heat generated by the circuitry.
One conventional dual band mixing technique is to use two separate mixers with separate IF outputs. The separate IF outputs are either combined or selected with a switching circuit. Unfortunately, such circuitry can be large for IF frequency and is particularly undesirable in MMIC applications.
In another conventional dual band mixing technique, the IF circuitry is duplicated for each RF band up to the point where the combination of the IF signals paths can be more easily implemented. However, this duplicate circuitry has the disadvantage of increasing the number of components.
Another conventional dual band mixer technique is to use a single classical mixer with switches at the RF and local oscillator (LO) ports. Using this technique, a single IF output can be achieved. Unfortunately, disadvantages of this technique are that the RF and LO switches can introduce losses and increase the amount of switch circuitry.
In one aspect, the invention is directed to a dual band mixer that has a common node for at least one radio frequency input and an intermediate frequency output. The dual band mixer also has a first transistor with a gate coupled to a first local oscillator input and a drain coupled to the common node, and a second transistor with a gate coupled to a second local oscillator input and a drain coupled to the common node.
Implementations of the invention may include one or more of the following features. The sources of the first and second transistors may be coupled to ground. The first and second transistors may be field effect transistors, e.g., depletion-type transistors. Circuitry may turn off the second transistor when a first local oscillator signal is applied to the gate of the first transistor and turn off the first transistor when a second local oscillator signal is applied to the gate of the second transistor. The circuitry may include a first network associated with the first transistor to generate a first negative voltage at a first node when the first local oscillator signal is applied to the gate of the first transistor and a second network associated with the second transistor to generate a second negative voltage at a second node when the second local oscillator signal is applied to the gate of the second transistor. The first network may include a first diode connected between the gate of the first transistor and the first node, and a first capacitor and a second diode connected in parallel between the source of the first transistor and the first node. Similarly, the second network may include a third diode connected between the gate of the second transistor and the second node, and a second capacitor and a fourth diode connected in parallel between the source of the second transistor and the second node. A common line may couple the first and second nodes. The circuitry need not require an external voltage source. A switch may direct one of a plurality of radio frequency inputs to the common node.
In another aspect, the invention is directed to a method of mixing in a dual band mixer. In the method, a gate of a first transistor is driven with a first local oscillator input, a gate of a second transistor is driven with a second local oscillator input, a radio frequency input is provided to a common node that is coupled to drains of the first and second transistors, and an intermediate frequency output is sensed from the common node.
In another aspect, the invention is directed to a dual band mixer that has a first transistor to mix a first local oscillator input signal with a first radio frequency signal, a second transistor to mix a second local oscillator input signal with a second radio frequency signal, and interconnection circuitry to turn off the second transistor when the first local oscillator input signal is applied to the first transistor and to turn off the first transistor when the second local oscillator input signal is applied to the second transistor.
Implementations of the invention may include one or more of the following features. Drains of the first and second transistors may be coupled to a common node for at least one of the first and second radio frequency input signals and an intermediate frequency output. The first and second transistors may be field effect transistors, e.g., depletion-type transistors. The interconnection circuitry may include a first network associated with the first transistor to generate a first negative voltage at a first node when the first local oscillator signal is applied to the gate of the first transistor and a second network associated with the second transistor to generate a second negative voltage at a second node when the second local oscillator signal is applied to the gate of the second transistor. The first network may include a first diode connected between the gate of the first transistor and the first node, and a first capacitor and a second diode connected in parallel between the source of the first transistor and the first node. The second network may include a third diode connected between the gate of the second transistor and the second node, and a second capacitor and a fourth diode connected in parallel between the source of the second transistor and the second node. A common line may couple the first and second nodes.
In another aspect, the invention is directed to a dual band mixer that has a plurality of transistors to mix a plurality of local oscillation input signals with a plurality of radio frequency signals, and interconnection circuitry coupling the plurality of transistors configured to turn off transistors other than one transistor at which a local oscillation input signal is received.
In another aspect, the invention is directed to a method of mixing in a dual band mixer. In the method, a first local oscillator input signal is mixed with a first radio frequency signal at a first transistor and a second local oscillator input signal is mixed with a second radio frequency signal at a second transistor. The second transistor is turned off when the first local oscillator input signal is applied to the first transistor, and the first transistor is turned off when the second local oscillator input signal is applied to the second transistor.
Potential advantages of the invention may include one or more of the following. The mixing circuitry can reduce signal losses, and can be realized with a small number of components. The mixing circuitry can have a single IF output without requiring a switch for the LO input signals. In addition, the mixing circuitry can provide a negative voltage output for use in surrounding circuitry.